Planck2015 results

Abstract

We compute and investigate four types of imprint of a stochastic background of primordial magnetic fields (PMFs) on the cosmic microwave background (CMB) anisotropies: the impact of PMFs on the CMB temperature and polarization spectra, which is related to their contribution to cosmological perturbations; the effect on CMB polarization induced by Faraday rotation; the impact of PMFs on the ionization history; magnetically-induced non-Gaussianities and related non-zero bispectra; and the magnetically-induced breaking of statistical isotropy. We present constraints on the amplitude of PMFs that are derived from different Planck data products, depending on the specific effect that is being analysed. Overall, Planck data constrain the amplitude of PMFs to less than a few nanoGauss, with different bounds that depend on the considered model. In particular, individual limits coming from the analysis of the CMB angular power spectra, using the Planck likelihood, are B 1 Mpc < 4.4 nG (where B 1 Mpc is the comoving field amplitude at a scale of 1 Mpc) at 95% confidence level, assuming zero helicity. By considering the Planck likelihood, based only on parity-even angular power spectra, we obtain B 1 Mpc < 5.6 nG for a maximally helical field. For nearly scale-invariant PMFs we obtain B 1 Mpc < 2.0 nG and B 1 Mpc < 0.9 nG if the impact of PMFs on the ionization history of the Universe is included in the analysis. From the analysis of magnetically-induced non-Gaussianity, we obtain three different values, corresponding to three applied methods, all below 5 nG. The constraint from the magnetically-induced passive-tensor bispectrum is B 1 Mpc < 2.8 nG. A search for preferred directions in the magneticallyinduced passive bispectrum yields B 1 Mpc < 4.5 nG, whereas the compensated-scalar bispectrum gives B 1 Mpc < 3 nG. The analysis of the Faraday rotation of CMB polarization by PMFs uses the Planck power spectra in EE and BB at 70 GHz and gives B 1 Mpc < 1380 nG. In our final analysis, we consider the harmonic-space correlations produced by Alfvén waves, finding no significant evidence for the presence of these waves. Together, these results comprise a comprehensive set of constraints on possible PMFs with Planck data.

Constraints on primordial magnetic fields from magnetically-induced perturbations: current status and future perspectives with LiteBIRD and future ground based experiments

“…Using the Planck 2018 baseline alone we obtain B 1 Mpc < 3.4 nG with the addition BICEP/KECK data we have B 1 Mpc < 3.5 nG and B 1 Mpc < 2.9 nG when adding also the South Pole Telescope, all at 95% C.L.. The improvement with respect to previous results with Planck 2015 [79] is mainly due to the combination of improved data on polarization by Planck 2018 and the improvement in our methodology. The results for specific configurations of the PMFs are the following: for n B = 2 is B 1 Mpc < 3 pG at 95% C.L.…”

“…[186]) show that there might still be some residual contamination on large angular scales even after cleaning. Previous studies on small angular scales have already shown how the analogous residuals degrade the constraints on PMFs amplitude [79,157], the update of these studies on large angular scale polarization in the context future experiments is in progress. It will be interesting to study the status and perspectives for another key signature from PMFs on CMB polarization as the one from the post-recombination heating.…”

“…It is possible to generate fields with an helical contribution by several mechanisms [69][70][71][72] and numerical simulations show how the fields rapidly reach the maximally helical confinguration independentely from the initial conditions [73][74][75][76][77]. Last, but not least, helicity can leave imprints onto the Cosmic Microwave Background [78][79][80][81][82][83].…”

“…The different imprints come from different mechanisms where PMFs play a dominant role. The dissipation of PMFs after recombination significantly affects T and E mode polarization through the modification of the ionization history [79,98,99,101]. This effect is very powerful in constraining the PMFs amplitude but is based on several assumptions which are necessary to perform the calculations, future numerical simulations on the interested scales will shed light on the robustness of these assumptions.…”

“…Current high sensitivity observations are mainly oriented to the high frequencies with high sensitivity low frequency observations limited to large angular scales where the Faraday signal is lower. For this reason current Faraday constraints are not competitive with other effects being in the rage of hundreds of nGauss [79,135,136], but Faraday rotation represents a very good target for future ground based observatories like the QUIJOTE and STRIP experiments [137,138] with a good potential also for small scale experiments on higher frequencies thanks to the very high sensitivities [139] but all must first account for decontamination from the Galactic Faraday rotation which currently sits at the 10 nG level [140].…”